How To Insulate Ductwork In Garage

How To Insulate Ductwork In Garage

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How to Insulate Ductwork – Step-by-Step Instructions

General Recommendations

  • Check the system and your home for any problems

Some things need to be taken care of ahead of time. Before insulating the ductwork, make sure to fix any structural problems within the house and damaged ducts, and get rid of mold and asbestos.

Of course, you would have to take all the health and safety issues into consideration.

  • The surface has to be clean and dry

Make sure that the ductwork is not covered in dust and that there is no moisture. Otherwise, the sealants and insulation might not be as effective.

  • Find the leaks

Keep the system running and carefully examine it. Mark any holes and also the spots that have become discolored or have rust on them (they indicate a possible future leak).

  • Protect yourself

If you are insulating ductwork yourself, you have to know how to protect yourself. When working with fiberglass, for example, you should wear goggles, an approved dust mask, and protective clothing. Ideally, you would want to have gloves, but we do understand that it might be challenging to do the job while wearing them.

How to Seal Ductwork

Experts recommend sealing your ductwork before getting the insulation installed. This additional step will bring plenty of benefits in the future. If the ductwork has been sealed, your insulation is going to be more effective and will serve for longer.

Leaks are most commonly found at joints or connections and at vents and registers where they come into the room. Sealing all the leaks is incredibly important, but is far more critical in the unconditioned areas.

Once you have marked the leaks and made sure that the surfaces are clean and dry, you can start sealing using one or more sealants.

  • Mastic is a paste that can be easily spread on holes and any gaps. Use gloved fingers or a stiffed paintbrush to apply the substance. The layer has to be about nickel-thick, in order for the sealant to work its magic.
  • You might want to use mesh in combination with mastic, in case the gaps are over an eighth of an inch wide.
  • Some choose to use butyl duct tape or foil duct tape. By the way, there are foil tapes are mastic tapes. Otherwise, you can use both mastic and any of the tapes mentioned. 

Warning! Old-fashioned duct tape is not a good fit for the job.

After you have sealed all the right places, make sure to double-check the whole system. Perform an air-flow test and a combustion safety test. Let the mastic dry, if you have used any, and only then continue with installing insulation.

How to Insulate Rectangular Ductwork

Rectangular ductwork is sometimes referred to as ‘sheet metal ducts’. It is, perhaps, the most popular type as it is relatively inexpensive to install. Unfortunately, such ducts are pretty ineffective – they are prone to leakage and condensation and allow excess noise in the house.

You should definitely install insulation around su

You should definitely install insulation around such ducts to make them much more effective.

Tip: use a measurement tape to understand how much material you are going to actually need. Don’t forget to allow some room for when insulating ducts in cramped places as you would usually need more material for such spots.

First things first, you have to check the speed of the blower motor. If the speed is too high, you can switch the wires to reduce it.

Use a simple utility knife to cut your insulation to the right size. After you have wrapped the material around the duct, make sure to pinch the seam closed. You can use short strips of foil tape to secure the seams or go for mechanical fasteners.

In case you are using tape, apply a long strip of it along the first short strip.

Hint: you can get hollow-core foam insulation – the thing is easy to install as it self-seams.

You may also choose preformed duct insulation.

All you would have to do to install it is disconnect the elbow to get the end of the duct exposed, then snap a cap onto the end and slip the insulation over the duct. Gently pull the material to get the whole length covered. 

How to Insulate Flexible Ductwork

The majority of manufacturers cover the wire coil and the bendable plastic that flexible ductwork is made out of with fiberglass insulation. So, in a lot of cases, you wouldn’t have to worry about insulating this part of your ductwork.

The great thing about flex ducts is that they redu

The great thing about flex ducts is that they reduce the number of joints and eliminate the need for offsets and elbows. 

Such ducts have to be sealed with duct mastic and held in place with tie wraps. This will help avoid thermal loss.

Tip: all supports have to be at least 1.5 inches wide. Make sure that they do not constrict the insulation as this may cause condensation.

If you ever decide to add another layer of insulation to your flex ductwork, follow the same instructions as for sheet metal ducts. It shouldn’t be too challenging, in case the flexible ductwork was installed correctly (without too many bends and kinks).

How to Insulate Ductwork Elbows

Insulating ductwork elbows can be tricky because of the angles that they bend at. You should definitely go for flexible insulation for this job.

  • The first thing that you want to do is clean the elbow junction. You can use a wire brush or sandpaper to rub it down.
  • Use an old rag to wipe the elbow dry and clean.
  • Measure the girth of the elbow and the length from top to bottom. After that, measure and cut the insulation
  • Make sure that the foil side of the material is facing outward. Use one hand to wrap the insulation around the elbows and the other to apply a short strip of tape along the seam

Hint: to make things a bit easier, you can cut the piece of insulation once again and apply one part on the top of the elbow and the second one – on the bottom.

  • Use longer strips of tape to secure all the seams

Warning! The insulation has to be tight but not compressed. If you press the material into the ductwork, you are going to reduce its effectiveness. 


Do you have to insulate metal ductwork?

Ducts tend to be made of thin material, usually sheet metal or fiberglass, which is why it is so easy for the air traveling through them to be lost. The ductwork in unconditioned areas, such as basements, floors, and ceilings is where ductwork insulation is most necessary.

Is insulating ductwork worth it?

The answer to the question of, “Should I insulate the ductwork in my basement?” is…. While insulating basement ductwork will, in fact, reduce energy loss from your ducts, thereby lowering the time your system has to run to properly cool or heat your house, it will also tend to make your basement cooler.

What’s The Alternative?

A dependable, lasting, energy-saving solution to the problem is to improve your home’s insulation. This is sometimes referred to as “improving the envelope”.

Good insulation provides a permanent barrier against unwanted airflow from the outside and the excessive levels of heat and cold that airflow brings. The better insulation your home has, the easier it is to maintain a consistently comfortable temperature, and the less it will cost you to do so.

As we’ve mentioned, the space above your garage is probably not as well insulated as the rest of your house. Correcting this problem by insulating the floor between the room and the garage below, as well as the insulation along the attic knee walls can make a big difference in the heating and cooling retention of that above-garage space, as well as the rest of your upstairs rooms.

Outdoor Ductwork Insulation

You should consider installing exterior ductwork insulation or insulating any outside ducts with a minimum of R-8.0 insulation. In case you live in climate zones 5-8, a minimum of R-12 is required.

Image source:

Image source:

A lot of outdoor duct systems come pre-insulated. If you want to add an additional layer, you would have to make sure that the material is durable, tear-resistant, and weatherproof

What Can Be Done To Solve This Cold Floor Hot Room Problem?

The three elements lacking in the potentially usable space above a garage are ductwork, air sealing and insulation.

When houses are built, the empty space above the garage is not usually thought of as a living area, so HVAC contractors don’t usually install ductwork to these areas. If they do install ductwork, it may be inadequate to meet the needs of this very airy space that is usually lacking in insulation.

The reason for this is that builders don’t usually insulate the floor of the empty space above an attached garage. In fact, they may not even insulate “knee walls”. This is the shared wall between the empty space and an upstairs room, such as a bedroom. This can cause heating and cooling problems in the adjoining room, as well.

These two circumstances combined can make it very difficult, if not impossible, to keep the temperature in an above-garage living space comfortable. The solution to the problem is twofold. Air circulation to the space must be increased, and insulation must be improved.

Step-By-Step Insulation Process

Keeping your garage well maintained can give you extra storage for many things. But it’s not easy. You have to keep it clean, level the garage slope, and now insulate ductwork. 

Insulation saves energy and keeps your home temperature in check. And let’s not forget, it gives your air-conditioner a bit of peace.  

They need a little place to breathe with all the air conditioning they do. Well, even if this pun doesn’t hit the spot for you, the easy guide to insulate your duct will. 

Here go the steps:

Repairing Leaks in Ductwork 

The whole insulation process will be pointless if there are leaks in the ducts. Even after the insulation, the air leak will harm the air conditioner.

Let’s go step by step to cover all bases:

Step 1: Finding the Leak

Detecting leaks is a piece of cake. 

Firstly, turn on your HVAC system. Then, try to feel along the ducts for any kind of leakage. You should focus on the joints and rusty areas. 

Smaller leaks are hard to detect. So, mark the leak immediately, as soon as you find them. Then turn off the system. 

Step 2: Picking the Right Sealant

Sealant preference varies due to product material and resistance. Both foil and mastic tape works great in this case. And if the leak is too big, you can always use liquid mastic with a brush. 

No matter how small the leak is, don’t use duct tape. They tend to give away pretty easily in extreme heat.  

Here are some of our favorite sealants we prefer using:

Recommended Products



Don’t forget to clean the ducts before you start sealing as well. Because dust can weaken the sealant’s bond.   

Step 3: Covering the Leak

Now that you have picked the sealant, let’s start sealing. Cover all the leaks with the tape and put an extra layer of taping on the joints. Even if there are no leaks. Being generous with layers will ensure no leaking in the future.  

You can even use your hands or a brush to secure the tape.  

Insulating Ductwork

After covering all the leaks, it’s time to attach the insulation. Remember the procedure is almost similar to insulating your basement or attic. So, let’s get to it.

Step 1: Cutting the Insulation 

Finally, it’s time to cut that insulation and place them right. To do so, use a sharp utility knife. And make the piece a little larger than the duct in size. You might need to run ductwork perpendicular to joists.

This is so it can overlap the seams. So, there’ll be no place for exposure. 

Step 2: Checking the Right Placement Of Insulation

In all haste, don’t forget to check whether the insulation is facing the right way. You don’t want to finish and then find out the placement is all wrong. 

Make sure the fiberglass side is on the ducts. Also, check that the vapor barrier is on the outside.

Step 3: Covering Insulation with Tape

Let’s start wrapping that insulation now. Firstly, place several small tapes along the seams to cover it entirely. And then, use a large tape to cover from top to bottom. 

Don’t forget to apply the same procedure in between the pieces. 

You can even do this for your already insulated ducts. If the previous insulation is in good shape, you can just add another layer over it. Otherwise, remove the previous layer to work on it. 

Follow the same steps even after moving your garage. And you’re good to go!

Tip: Don’t press the insulation too tight. The R-value of the insulation depends on the air space inside the fiber. And, it may drop a few levels if the air space is compromised.

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